Mobile communication method and mobile station

ABSTRACT

A mobile communication method includes the steps of transmitting a first control signal including an identifier different from a C-RNTI to the mobile station UE#A through a FDCCH by a radio base station PhNB# 10  managing a cell # 10  formed by linking multiple small cells, transmitting a second control signal including an identifier to the mobile station UE through a PDCCH by a radio base station eNB# 1  managing a cell # 1  having a coverage area overlapping with a coverage area of the cell # 10 , and regarding the first control signal as valid by the mobile station UE#A, when it determines that the identifier included in the first control signal and the identifier included in the second control signal match each other.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.14/420,907 filed Feb. 11, 2015, which is a national stage application ofPCT/JP2013/072049 filed on Aug. 19, 2013, which claims priority toJP2012-188687 filed on Aug. 29, 2012.

TECHNICAL FIELD

The present invention relates to a mobile communication method and amobile station.

BACKGROUND ART

In LTE (Long Term Evolution), a radio base station eNB is configured totransmit/receive data to and from a mobile station UE performingcommunications in a cell under the control thereof, with a C-RNTI(Cell-Radio Network Temporary Identify) allocated to the mobile stationUE as illustrated in FIG. 6 (see, non-patent document 1).

The C-RNTI is allocated on a cell-by-cell basis. In LTE, as illustratedin FIG. 6, a same C-RNTI cannot be allocated to a mobile station UE#1and a mobile station UE#2 which perform communications in a same celland a same C-RNTI can be allocated to a mobile station UE#1 (or a mobilestation UE#2) and a mobile station UE#3 which perform communications indifferent cells #A/#B.

Here, the C-RNTI is allocated in “Contention based RA (Random Access)Procedure” or a handover procedure.

In addition, the radio base station eNB is configured to assignresources for transmitting downlink data or uplink data by using theC-RNTI allocated to the mobile station UE.

Meanwhile, in the “Rel-12 workshop” of the 3GPP, many proposals on“Small cell enhancement” have been made as topics of FRA (Future RadioAccess).

In such proposals, a concept of “Phantom cell” has been discussed.

As illustrated in FIG. 7, unlike a conventional macro cell, a phantomcell can cover a wider area by linking many “small cells” to form onelarge cell.

PRIOR ART DOCUMENT Non-Patent Document

Non-patent document 1: 3GPP TS36.300

SUMMARY OF THE INVENTION

However, as illustrated in FIG. 8, 65535 C-RNTIs are managed in eachcell (a macro cell and a phantom cell), and one C-RNTI has to beallocated to each mobile station UE.

Here, when the coverage area of the phantom cell becomes wider, thenumber of mobile stations UE performing communications in the phantomcell increases. Accordingly, envisaged is a problem of causing a case inwhich the phantom cell may run out of C-RNTIs allocatable to the mobilestations UE.

In a conceivable operation for solving the above-described problem, asillustrated in FIG. 9, one C-RNTI is allocated to each mobile station UEin a macro cell, while one C-RNTI is allocated to multiple mobilestations UE in a phantom cell (in other words, one C-RNTI is sharedbetween the multiple mobile stations UE).

However, execution of the above-described operation entails a problemthat mobile stations UE to which the same C-RNTI is allocated in thesame cell may collide with each other. Here, when such a collisionoccurs, a mobile station UE which is not intended by the radio basestation eNB may wrongly receive allocation information for a correctmobile station UE.

For this reason, the present invention is made in view of theabove-described problem. Accordingly, an objective of the presentinvention is to provide a mobile communication method and a mobilestation capable of, even when a same C-RNTI is allocated to multiplemobile stations UE#A to UE#D in a phantom cell, avoiding a collisionbetween the mobile stations UE#a to UE#D to which the same C-RNTI isallocated.

A first feature of the present invention is summarized as a mobilecommunication method, including the steps of: transmitting a firstcontrol signal including an identifier different from a cell-specificidentifier to a mobile station through a physical downlink controlchannel by a first radio base station managing a phantom cell formed bylinking multiple small cells; transmitting a second control signalincluding an identifier to the mobile station through a physicaldownlink control channel by a second radio base station managing a macrocell having a coverage area overlapping with a coverage area of thephantom cell; and regarding the first control signal as valid by themobile station, when the mobile station determines that the identifierincluded in the first control signal and the identifier included in thesecond control signal match each other.

A second feature of the present invention is summarized as a mobilestation capable of communicating with a first radio base stationmanaging a phantom cell formed by linking multiple small cells and asecond radio base station managing a macro cell having a coverage areaoverlapping with a coverage area of the phantom cell, the mobile stationincluding: a reception unit configured to receive a first control signalincluding an identifier different from a cell-specific identifier fromthe first radio base station through a physical downlink control channeland receive a second control signal including an identifier from thesecond radio base station through a physical downlink control channel;and a determination unit configured to regard the first control signalas valid when determining that the identifier included in the firstcontrol signal and the identifier included in the second control signalmatch each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an entire configuration diagram of a mobile communicationsystem according to a first embodiment of the present invention.

FIG. 2 is a functional block diagram of a radio base station PhNB#10according to the first embodiment of the present invention.

FIG. 3 is a diagram for illustrating operations of radio base stationsPhNB#10/eNB#1 and mobile stations UE#A/UE#B according to the firstembodiment of the present invention.

FIG. 4 is a functional block diagram of the radio base station eNB#1according to the first embodiment of the present invention.

FIG. 5 is a functional block diagram of a mobile station UE according tothe first embodiment of the present invention.

FIG. 6 is a diagram for illustrating a conventional technology.

FIG. 7 is a diagram for illustrating the conventional technology.

FIG. 8 is a diagram for illustrating the conventional technology.

FIG. 9 is a diagram for illustrating the conventional technology.

DETAILED DESCRIPTION

(Mobile Communication System According to the First Embodiment of thePresent Invention)

A mobile communication system according to a first embodiment of thepresent invention will be described with reference to FIGS. 1 to 5.

As illustrated in FIG. 1, a mobile communication system according to thepresent embodiment is an LTE mobile communication system, which includesa radio base station PhNB#10 configured to manage a cell #10, a radiobase station eNB#1 configured to manage a cell #1, a radio base stationeNB#2 configured to manage a cell 12, and a radio base station eNB#3configured to manage a cell #3.

Here, the cell #10 is a phantom cell formed by linking multiple smallcells and the cells #1 to #3 are macro cells.

As illustrated in FIG. 1, a coverage area of the cell #10 and coverageareas of the cells #1 to #3 are deployed to at least partially overlapeach other.

As illustrated in FIG. 2, the radio base station PhNB#10 according tothe present embodiment includes an allocation unit 11, a reception unit12, and a transmission unit 13.

The allocation unit 11 is configured to allocate a same C-RNTI_(ph) tothe mobile stations UE#A to UE#D in the cell #10.

Here, the allocation unit 11 may allocate a same C-RNTI_(ph) to apredetermined number of the mobile stations UE#A to UE#D in the cell#10.

In addition, the allocation unit 11 allocates an identifier differentfrom a C-RNTI to each of the mobile stations UE#A to UE#D in the cell#10.

Such an identifier can identify each of the mobile stations UE#A to UE#Dand be used in place of a UE-ID.

The reception unit 12 is configured to receive various kinds of signalsfrom the mobile stations UE#A to UE#D in the cell #10 and the radio basestations eNB#1 to eNB#3. The transmission unit 13 is configured totransmit various kinds of signals to the mobile stations UE#A to UE#D inthe cell #10 and the radio base stations eNB#1 to eNB#3.

Here, the transmission unit 13 notifies each of the mobile stations UE#Ato UE#D in the cell #10 of a C-RNTI_(ph) or an identifier, which isallocated by the allocation unit 11.

Also, the transmission unit 13 may notify the radio base stations eNB#1to eNB#3 of the identifier allocated to each of the mobile stations UE#Ato UE#D in the cell #10.

In addition, as illustrated in FIG. 3, the transmission unit 13transmits a first control signal including a C-RNTI and identifier foreach of the mobile stations UE#A to UE#D to each of the mobile stationsUE#A to UE#D in the cell #10 through a PDCCH (Physical Downlink ControlChannel).

Instead, the transmission unit 13 may transmit the first control signalincluding the C-RNTI and identifier for each of the mobile stations UE#Ato UE#D through an ePDCCH (enhanced Physical Downlink Control Channel).

The configurations of the radio base stations eNB#1 to eNB#3 accordingto the present embodiment are basically same, and the description willbe mainly given below to the configuration of the radio base stationeNB#1.

As illustrated in FIG. 4, the radio base station eNB#1 according to thepresent embodiment includes a reception unit 21, a management unit 22,and a transmission unit 23.

The reception unit 21 is configured to receive various kinds of signalsfrom the mobile stations UE#A to UE#D and the radio base stationPhNB#10.

For example, the reception unit 21 receives identifiers for the mobilestations UE#A to UE#D in the cell #10 from the radio base stationPhNB#10.

The management unit 22 is configured to manage identifiers for themobile stations UE#A to UE#D in the cell #10 which are received by thereception unit 21.

The transmission unit 23 is configured to transmit various kinds ofsignals to the mobile stations UE#A to UE#D and the radio base stationPhNB#10.

For example, as illustrated in FIG. 3, the transmission unit 23transmits a second control signal including an identifier for each ofthe mobile stations UE#A to UE#D to each of the mobile stations UE#A toUE#D in the cell #10 through the PDCCH.

Here, the second control signal may be a dummy control signal only fortransmitting an identifier for each or the mobile stations UE#A to UE#Dwithout allocation information and the like.

The configurations of the mobile stations UE#A to UE#D according to thepresent embodiment are basically same, and the description will bemainly given below to the configuration of the mobile station UE#A.

As illustrated in FIG. 5, the mobile station UE#A according to thepresent embodiment includes a reception unit 31, a determination unit32, and a transmission unit 33.

The reception unit 31 is configured to receive various kinds of signalsfrom the radio base stations PhNB#10/eNB#1/eNB#2/eNB#3. The transmissionunit 33 is configured to transmit various kinds of signals to the radiobase stations PhNB#10/eNB#1/eNB#2/eNB#3.

For example, the reception unit 31 receives a C-RNTI_(ph) or identifierwhich is allocated to the mobile station UE through a dedicated signalfrom the radio base station PhNB#10.

Also, the reception unit 31 may receive a first control signal (forexample, scheduling information) including an identifier for the mobilestation UE through the PDCCH using the C-RNTI_(ph) for the mobilestation UE#A from the mobile station PhNB#10.

Furthermore, the reception unit 31 may receive a second control signalincluding the identifier for the mobile station UE#A through the PDCCHusing the C-RNTI_(ph) for the mobile station UE#A from the radio basestations eNB#1 to eNB#3.

The determination unit 32 is configured to determine whether or not theidentifier included in the first control signal and the identifierincluded in the second control signal match each other or whether or notthe second control signal corresponding to the first control signal isreceived.

Here, the description “the identifiers match each other” may mean thatthe same identifier is received or may be intended to mean that theidentifiers associated with each other in advance are received.

Here, when determining that the identifier included in the first controlsignal and the identifier included in the second control signal matcheach other, the determination unit 32 regards the first control signalas valid.

In other words, in such a case, the transmission unit 33 transmits adata signal to the radio base station PhNB#10 through the PUSCH based onthe first control information (scheduling information) received by thereception unit 31 (or may activate a random access procedure or the likeinstructed through the PDCCH).

Instead, in such a case, the reception unit 31 may receive datatransmitted through the PDSCH based on the firs control information(scheduling information).

On the other hand, the determination unit 32 may discard or ignore thefirst control signal when determining that the identifier included inthe first control signal and the identifier included in the secondcontrol signal do not match each other.

In addition, in such a case, the determination unit 32 may discard orignore the second control signal.

Alternately, the determination unit 32 may discard or ignore the firstcontrol signal when the second control signal is not received after thefirst control signal is received.

In other words, in such a case, based on the first control information(scheduling information) received by the reception unit 31, thetransmission unit 33 does not transmit a data signal to the radio basestation PhNB#10 through the PUSCH or does not activate a procedure (forexample, random access procedure) instructed by the first controlinformation.

Also, in such a case, the reception unit 31 does not receive a datasignal transmitted from the radio base station PhNB#10 through the PDSCHbased on the first control information (scheduling information).

Furthermore, the determination unit 32 does not regard the secondcontrol signal received by the reception unit 31 as valid regardless ofwhether or not the identifier included in the first control signal andthe identifier included in the second control signal match each other.

In other words, the transmission unit 33 does not transmit a data signalto the radio base station PhNB#10 through the PUSCH or does not activatea procedure (for example, random access procedure) instructed by thefirst control information, based on the second control informationreceived by the reception unit 31.

Also, in such a case, the reception unit 31 does not receive the datasignal transmitted from the radio base station PhNB#10 through the PDSCHbased on the second control information.

In the example of FIG. 3, the mobile station UE#A determines that anidentifier X included in the first control signal received from theradio base station PhNB#10 and an identifier X included in the secondcontrol signal received from the radio base station eNB#1 match eachother and regards the first control signal as valid.

On the other hand, the mobile station UE#B determines that an identifierX included in the first control signal received from the radio basestation PhNB#10 and an identifier X included in the second controlsignal received from the radio base station eNB#1 do not match eachother, and discards the first control signal without regarding it asvalid.

The features of the present embodiment may also be expressed as follows.

A first feature of the present embodiment is summarized as a mobilecommunication method, including the steps of: transmitting a firstcontrol signal including an identifier different from a C-RNTI(cell-specific identifier) to a mobile station UE#A through a PDCCH(physical downlink control channel) by a radio base station PhNB#10(first radio base station) managing a call #10 (phantom cell) formed bylinking multiple small cells; transmitting a second control signalincluding an identifier to the mobile station UE through a PDCCH(physical downlink control channel) by a radio base station eNB#1(second radio base station) managing a cell #1 (macro cell) having acoverage area overlapping with a coverage area of the cell #10; andregarding the first control signal as valid by the mobile station UE,when the mobile station UE determines that the identifier included inthe first control signal and the identifier included in the secondcontrol signal match each other.

With the above-described configuration, even when a same C-RNTI_(ph) isallocated to the multiple mobile stations UE#A to UE#D in the cell #10,each of the mobile stations UE#A to UE#D can determine whether or notthe control signal is addressed to the mobile station UE itself by usingthe identifiers transmitted from the radio base station PhNB#10 and theradio base station eNB#1.

in the first feature of the present embodiment, the mobile communicationmethod may include the step of discarding or ignoring at least one ofthe first control signal and the second control signal by the mobilestation UE, when the mobile station UE determines that the identifierincluded in the first control signal and the identifier included in thesecond control signal do not match each other.

With the above-described configuration, each of the mobile stations UE#Ato UE#D discards the control signal when determining that the controlsignal is not addressed to the mobile station UE itself. Thus, even whenthe same C-RNTI_(ph) is allocated to the multiple mobile stations UE#Ato UE#D in the cell #10 the radio base station PhNB#10 can transmit thecontrol signal to a proper one of the mobile stations UE#A to UE#D.

In the first feature of the present embodiment, the mobile communicationmethod may include the step of discarding the first control signal bythe mobile station UE, when the mobile station UE does not receive thefirst control signal or the second control signal including theidentifier included in the first control signal.

In the first feature of the present embodiment, the mobile station UEdoss not have to regard the second control signal as valid, regardlessof whether or not the identifier included in the first control signaland the identifier included in the second control signal match eachother.

With the above-described configuration, the radio base station eNB#1 cannotify each of the mobile stations UE#A to UE#D in the cell #10 of theidentifier with a minimum data amount without notifying needlessinformation.

In the first feature of the present embodiment, the mobile station UEmay determine whether or not the identifier included in the firstcontrol signal and the identifier included in the second control signalmatch each other when there is an instruction from the radio basestation eNB.

In the first feature of the present embodiment, the mobile station UEmay receive the first control signal or the second control signalincluding the identifier included in the first control signal in a celldesignated by the radio base station eNB.

A second feature of the present embodiment is summarized as a mobilestation UE capable of communicating with a radio base station PhNB#10managing a cell #10 formed by linking multiple small cells and a radiobase station eNB#1 managing a cell #1 having a coverage area overlappingwith a coverage area of the cell #10, the mobile station UE including: areception unit 31 configured to receive a first control signal includingan identifier different from a C-RNTI from the radio base stationPhNB#10 through a PDCCH and receive a second control signal including anidentifier from the radio base station enB#1 through a PDCCH; and adetermination unit 32 configured to regard the first control signal asvalid when determining that the identifier included in the first controlsignal and the identifier included in the second control signal matcheach other.

With the above-described configuration, even when the same C-RNTI_(ph)is allocated to the multiple mobile stations UE#A to UE#D in the cell#10, each of the mobile stations UE#A to UE#D can determine whether ornot the control signal is addressed to the mobile station UE itself, byusing the identifiers transmitted from the radio base station PhNB#10and the radio base station eNB#1.

In the second feature of the present embodiment, the determination unit32 may discard or ignore at least one of the first control signal andthe second control signal when determining the identifier included inthe first control signal and the identifier included in the secondcontrol signal do not match each other.

With the above-described configuration, each of the mobile stations toUE#D discards the control signal, when determining that the controlsignal is not addressed to the mobile stations UE itself. Thus, evenwhen the same C-RNTI_(ph) is allocated to the multiple mobile stationsUE#A to UE#D in the cell #10, the radio base station PhNB#10 cantransmit the control signal to a proper one of the mobile stations UE#Ato UE#D.

In the second feature of the present embodiment, the determination unit32 may discard the first control signal when the first control signal orthe second control signal including the identifier included in the firstcontrol signal is net received.

In the second feature of the present embodiment, the determination unit32 does not have to regard the second control signal as valid regardlessof whether or not the identifier included in the first control signaland the identifier included in the second control signal match eachother.

With the above-described configuration, the radio base station eNB#1 cannotify each of the mobile stations UE#A to UE#D in the cell #10 of theidentifier with a minimum data amount without notifying needlessinformation.

In the second feature of the present embodiment, the determination unit32 may determine whether or not the identifier included in the firstcontrol signal and the identifier included in the second control signalmatch each other when there is an instruction from the radio basestation eNB.

In the second feature of the present embodiment, the determination unit32 may receive the first control signal or the second control signalincluding the identifier included in the first control signal in a celldesignated by the radio base station eNB.

Also, the collision avoiding control described above needs to beperformed only when assignment is simultaneously made (the schedulinginformation is transmitted) to the mobile stations UE to which the sameidentifier is allocated in the same cell, and does not need to be alwaysperformed.

In other words, the mobile station UE may perform the collision avoidingcontrol as described above only when an instruction to perform suchcontrol is issued by the radio base station eNB.

The designation may be performed in any layer of the RRC layer, PDCPlayer, RLC layer, MAC layer, and physical layer. In particular, thedesignation may be notified together with the first control signal ormay be notified together with the second control signal.

Furthermore, in the above description, a cell to transmit the secondcontrol signal is described as a macro cell, but the second controlsignal may be received by any cell in which a mobile station UE is set.

It should be noted that the foregoing operations of the mobile stationsUE#A to UE#D and the radio base stations eNB#1/eNB#2/eNB#3/PhNB#10 maybe implemented by hardware, may be implemented by a software moduleexecuted by a processor, or may be implemented in combination of thetwo.

The software module may be provided in a storage medium in any format,such as a RAM (Random Access Memory), a flash memory, a ROM (Read OnlyMemory), an EPROM (Erasable Programmable ROM), an EEPROM (ElectronicallyErasable and Programmable ROM), a register, a hard disk, a removabledisk, or a CD-ROM.

The storage medium is connected to a processor so that the processor canread and write information from and to the storage medium. Instead, thestorage medium may be integrated in a processor. The storage medium andthe processor may be provided inside an ASIC. Such an ASIC may beprovided in the mobile stations UE#A to UE#D and the radio base stationseNB#1/eNB#2/eNB#3/PhNB#10. Otherwise, the storage medium and theprocessor may be provided as discrete components inside the mobilestations UE#A to UE#D and the radio base stationseNB#1/eNB#2/eNB#3/PhNB#10.

Hereinabove, the present invention has been described in detail by useof the foregoing embodiments. However, it is apparent to those skilledin the art that the present invention should not be limited to theembodiments described in the specification. The present invention can beimplemented as an altered or modified embodiment without departing fromthe spirit and scope of the present invention, which are determined bythe description of the scope of claims. Therefore, the description ofthe specification is intended for illustrative explanation only and doesnot impose any limited interpretation on the present invention.

Note that the entire content of Japanese Patent Application No.2012-188687 (filed on Aug. 29, 2012) is incorporated by reference in thepresent specification.

INDUSTRIAL APPLICABILITY

As described above, the present invention can provide a mobilecommunication method and a mobile station, in which a collision betweenmobile stations UE#A to UE#D to which a same C-RNTI is allocated can beavoided even when the same C-RNTI is allocated to the multiple mobilestations UE#A to UE#ID in a phantom cell.

EXPLANATION OF REFERENCE NUMERALS

eNB#1, eNB#2, eNB#3, PhNB#10 radio base station

11 allocation unit

12, 21, 31 reception unit

13, 23, 33 transmission unit

22 management unit

32 determination unit

1. A mobile communication method, comprising steps of: transmitting, bya first radio base station managing a cell formed with a plurality ofsmall cells, an identifier to a second radio base station managing amacro cell having a coverage area overlapping with a coverage area ofthe cell; transmitting, by the second radio base station, a controlsignal including the identifier to a mobile station through a physicaldownlink control channel; and performing, by the mobile station, arandom access procedure with the first radio base station based on theidentifier.
 2. A mobile station capable of communicating with a firstradio base station managing a cell formed with a plurality of smallcells and a second radio base station managing a macro cell having acoverage area overlapping with a coverage area of the cell, the mobilestation comprising: a receiver that receives from the second radio basestation through a physical downlink control channel, a control signalincluding an identifier transmitted from the first radio base station;and a processor that performs a random access procedure with the firstradio base station based on the identifier.
 3. A mobile communicationmethod; comprising steps of: transmitting, by a first radio base stationmanaging a cell formed with a plurality of first cells, an identifier toa second radio base station managing a second cell having a coveragearea overlapping with a coverage area of the cell; transmitting, by thesecond radio base station, a control signal including the identifier toa mobile station through a physical downlink; control channel; andperforming, by the mobile station, a random access procedure with thefirst radio base station based on the identifier.